Measurement Computing ADAC/5500 Series - Manual (Page 35)

ADAC Series PCI Boards 795 - 30 - ADAC/5500 Series User Manual 928
5.2 THEORY OF OPERATION
5.2.1 Process Definitions
In order to best understand how to operate the various board functions, it is important to first understand the language
that will be used to describe the board processes. The following is a list of pertinent terms and definitions used in this
document.
ADC
Analog to Digital Converter, also referred to as A/D. This is the circuitry that samples the voltage present at one of the
inputs and translates that reading to a number that is representative of the input voltage. The number supplied by the
ADC is referred to as the ADC DATA or RAW DATA and its units are bits or binary digits.
DAC
Digital to Analog Converter, also referred to as D/A. This is the circuitry that translates a binary data word to a specific
voltage level. The optional DACs on the ADAC/5500 Series boards are specified for DC accuracy. The DACs on these
boards can be clocked and triggered; the outputs are updated as soon as they receive new data.
ADC Channel
This term is used to refer to any of the 256 addressable connections to the multiplexed ADC. The ADAC/5500MF has
8 on-board ADC channels available and supports the ADAC-TB-8 panel. The ADAC/5501MF, ADAC/5502MF,
ADAC/5503HR and ADAC/5504HR have 16 on-board channels available and support the ADAC-TB-16 and ADAC-
TB-8 panels for a maximum number of 256 input channels.
ADC Data- also Raw Data
This is the unscaled number returned by the ADC. For two’s complement data coding (which is standard for bipolar
inputs), this number will be either in the range of -2000...+1999 (for 12-bit A/D boards) or -32242…+32241 (for 16-bit
boards). For straight binary data coding (which is standard for unipolar inputs), this number will be in the range of
0..+3999 on 12-bit A/D boards and 0...+64483 on 16-bit boards. This number is typically multiplied by some scale
factor to convert the number to more useful engineering units. For example: the bipolar
±10 V input uses a scale factor
of .005 V/bit. An ADC reading of +1000 when multiplied by .005 V results in +5.000 V. Similarly, the 16 bit scale
factor for the
±10 V scale is .000130140 V/bit.
DAC Data- also Raw Data
This is the unscaled number sent to each DAC channel. For two’s complement data coding (which is standard for
bipolar inputs), this number will be either in the range of -32722...+32722. For straight binary data coding (which is
standard for unipolar inputs), this number will be in the range of 0..+65445. This number is typically multiplied by
some scale factor to convert the number to more useful engineering units. For example: 0-10 V input uses a scale factor
of .000152800V/bit. A DAC DATA value of 32723 when multiplied by .00015280 results in 5.000044 V at the DAC
output line.
ADC Conversion
This is the process of sampling a single input or transducer’s voltage and generating a representative data value.
DAC Conversion
This is the process of outputting a single voltage generated from representative data value.